This invention relates to acoustic line arrays and more particularly to a low-cost expendable acoustic line receiving array which is easily deployed and handled by virtue of its small diameter in both towed and fixed configurations.
Line acoustic receiving arrays presently in use consist of discrete acoustic sensors (hydrophone elements) spaced at intervals along the array. Such an array uses may individual hydrophones, in some cases as many as several hundred. Each hydrophone must have its output returned to the platform from which the array is deployed and where the signal processing electronics and readout equipment are located. The paths from the hydrophone to the platform end are established in some cases by simply wiring each hydrophone separately to the platform. This results in a large array diameter, typically 8 centimeters or so, with its attendant difficulties of handling and storing. Some array systems presently in use apply time or frequency multiplexing to reduce the number of conductors and hence the size of the cable. Multiplexing techniques, however, require electronics at each hydrophone location resulting in relatively high cost and lowered reliability. In either case, the individually wired array or multiplexed array, the presence of discrete hydrophone elements results in a relatively costly array vulnerable to damage to the delicate piezo-ceramic elements. Furthermore, to achieve satisfactory beam patterns, hydrophone elements must be spaced at intervals of less than half a wave length of the acoustic wave. In most cases the frequency response or directivity of the array is limited by this requirement. It is thus desirable to have an acoustic line array which is relatively inexpensive and can be easily deployed both in towed and fixed configurations.